Nitrile trimerization process

ABSTRACT

Aromatic nitriles, such as terephthalonitrile, isophthalonitrile, benzonitrile, etc., are trimerized to the corresponding 1,3,5-triazine by heating the nitrile in the presence of a copper carbonate catalyst.

Unitefi States Patent [191 Miller June 18, 1974 NITRILE TRIMERIZATION PROCESS Primary ExaminerJohn M. Ford [75] Inventor. Gordon H. Miller, Rlchmond, Va. Attorney g or Firm T H- y; C G Reis [73] Assignee: Texaco Inc., New York, NY.

[22] Filed: Dec. 29, 1972 [21] App]. No.: 319,600, [57] ABSTRACT [52 U5. Cl 260/248 CS A omat c n les, uc s tercphthalonitrile, s p [51] Int. Cl C07d 55/50 thalonitrile, benzonitrile, etc., are trimerized to the [58] Field of Search 260/248 CS, 78.4 N, 2 R corresponding 1,3,5-triazine by heating the nitrile in e the presence of a copper carbonate catalyst. [5 6] References Cited UNITED STATES PATENTS 14 Cl i No D n 3,763,115 10/1973 Miller 260/248 BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a process for preparing 1,3,5-triazines in high yield by trimerization of aromatic nitriles. More particularly, this invention relates to an improved process for the conversion of aromatic nitriles to the corresponding aromatic substituted 1,3,5-triazines in which the nitriles are heated with a catalyst at a temperature of about 180 to about 450C and afterward the unconverted monomer is removed from the triazine product by sublimation.

2. Description of the Prior Art The preparation of 1,3,5-triazines from aromatic nitriles, such as benzonitrile, etc., has been described in the literature. Trimerization of aromatic nitriles, for example, can be carried out catalytically or by employing heat alone, or heat and pressure. A wide variety of catalysts are known including hydrides and amides of the alkali metals and alkaline earth metals, sulfuric acid,

zinc diethyl, bromine, metallic sodium, zinc chloride,

aluminum chlrodie, titanium tetrachloride, antimony trichloride, nickel chloride, copper chloride, berrylium chloride, bismuth oxychloride, manganese chloride, cobalt chloride, manganese bromide, cobalt bromide,

.copper acetate, manganese acetate, vanadyl chloride,

tion of 1,3,5-triazines by'trimerization 0f, the corresponding aromatic nitriles suffer from a number of disadvantages. Most of the previously proposed processes are tedious to operate, a long reaction time is generally required, and it has been found especially difficult to conveniently remove the unconverted nitrile from the 1,3,5-triazine product. Toland in US. Pat. No. 3,060,179 removes unreacted nitrile from the reaction mixture by solvent extraction and then, at very'high temperatures (i.e., from 400 to 500 C) and at a relatively slow rate, sublimes the trimer.

DETAILED DESCRIPTION OF THE INVENTION The process of this invention is applicable tothe conversion of a wide variety of aromatic nitriles, including mononitriles, dinitriles and other polynitriles, to form aromatic substituted l,3,5-triazines.

Nitriles useful as starting materials in'the process of this invention include, for example, compounds of the formula:

wherein R is selected from the group consisting of. hy-

drogen, alkyl of from one to 10 inclusive carbon atoms as exemplified by methyl, ethyl, propyl, pentyl, heptyl, octyl and isomers thereof, amine, nitro, hydroxyl, carboxyl and halogen selected from the group consisting of chlorine, fluorine, iodine and bromine, and n is an integer of from one to four inclusive.

Among the nitriles which are suitable as starting materials in the method of this invention are benzonitrile,

2-toluonitrile, 3-toluonitrile, 4-toluonitrile, 3- ethylbenzonitrile, 4-t-butylbenzonitrile, 4- aminobenzonitrile, 3-aminobenzonitrile, 3- hydroxybenzonitrile, 3-nitrobenzonitrile, 4-ethyl2- nitrobenzonitrile, 2-hydroxy-3-propylbenzonitrile, 3- phenylbenzonitrile, 2,4-dimethylbenzonitrile, 2,6-diethylbenzonitrile, 3-chlorobenzonitrile, 4- bromobenzonitrile, 3-fluorobenzonitrile, I naphthonitrile, 2-naphthonitrile, I l-naphthonitrile,

3-methyl-1-naphthonitrile, 3-chloro-1-naphthonitrile, 4-nitro- 1 -naphthonitrile, 2-hydroxy- I -naphthonitrile, 4-hydroxy-2-methyll -naphthonitrile, 4-fluoro-2- naphthonitrile, orthophthalonitrile, isophthalonitrile, terephthalonitrile, 3-methyl-l-4-dicyanobenzene, 5- isopropyl-l ,3-dicyanobenzene, 2,5-dimethyl-l 4- dicyanobenzene, 2-chloro-1,3-dicyanobenzene, 5-bromo-1,4-dicyanobenzene, S-amino-I ,3- dicyanobenzene, 3-nitrol -2dicyanobenzene,

4-hydroxyl ,3-dicyanobenzene, 2-(dichloromethyl )-v 1,3-dicyanobenzene, 5-( chloromethyl )-1 ,4- dicyanobenzene, 2-ethyl-3-chIoro-l ,4- dicyanobenzene, 3-nitro-1,2-dicyanobenzene, 1,3 ,5

tricyanobenzene, 2-chloro-l,3,5-tricyanobenzene, 3-

tetracyanobenzene. Mixtures of the above-mentioned aromatic nitriles, such as a mixture of about 66 percent by weight of isophthalonitrile and about 34 percent by weight of terephthalonitrile can be employed in this process, if desired. 1

An especially suitable group of starting materials includes nitriles of the formula (1) above where n is an integer of from 1 to 2 inclusive. Examples of materials in this last-mentioned category include isophthalonitrile (i.e., 1,3-dicyanoberizene) and terephthalonitrile (i.e. 1,4-dicyanobenzene). In addition to the examples shown above, other substituted nitriles can be employed, for example, those contained in groups derived from a carboxyl group, such as carboxylic salts, amides and esters as well as sulfone and sulfonic acid groups. In this specification the term nitrile is used to refer to compounds having one or more cyano groups attached to the carbon atoms of the aromatic ring.

In this process the temperature at which the trimerization reaction is conducted can be varied over a wide range. Generally, the temperature employed will be from about to about 450 and, preferably, from about 200 to about 425 C. The reaction time will vary widely depending upon the nature of specific nitrile used and the reaction conditions employed, although a satisfactory yield of the product can be achieved in the quantity of the catalyst employed will be from about 0.1 percent by weight up to about 50 percent by weight based on the weight of the nitrile charged to the reactor and preferably will be from about 0.1 percent by weight up to about percent by weight on the same basis. Preferably, the reaction is carried out in the absence of air or in the presence of an inert gas which can be, for example, nitrogen, argon, helium, etc. Mixtures of these same inert gases may be employed, if desired. The process of this invention can be conducted under a pressure less than atmospheric or pressures of about atmospheric to about 2000 psi may be utilized. Preferably, the pressure will be from about atmospheric to.

about 500 psi.

Catalysts suitable for use in the process of this invention include:

1. CuCO Cu(Ol-l) 2. 2CuCO Cu(Ol-l) and 3. mixtures of l) and (2).

An important facet of this invention is that after the conversion operation has been completed the unreacted nitrile may be removed overhead from the reaction mixture by sublimation, leaving as bottoms the trimer which is available for further polymerization to a B-stage (partially cured) polymer and to the fully cured polymeric product. This sublimation scheme can be applied to purification of the trimer product whether the reaction is carried out at atmospheric or at higher pressures. Alternatively, the unreacted nitrile can be removed from the reaction mixture by extraction with a solvent, such as ethyl ether, acetone, acetonitrile, etc.

It is economically advantageous to conduct the reaction under pressure, so that when the trimer conversion is optimum the temperature can be maintained while the pressure is reduced to atmospheric or to a partial vacuum. If desired, an inert gas can be employed in the sublimation operation, and in this case the inert gas or mixture of inert gas is blownthrough the heated reaction mixture to sublime out all of the unconverted monomer.

Since the catalysts of this invention are nonvolatile materials they will remain in the trimer product at the conclusion of the sublimation operation or at the conclusion of the trimerization reaction, and in the case of an aromatic substituted 1,3,5-triazine formed from a dinitrile, the trimer product together with the included catalyst and with additional catalyst as required, may then be employed to prepare a B-stage polymer, following which the product may be cured to a final state. The

catalysts may be removed from the trimer before or after sublimation by a solvent wash with materials such as acetone, acetonitrile, ethyl ether, water, ammonium hydroxide, etc.

The triazine products of this invention prepared from dinitriles can, as previously pointed out, be further polymerized in the presence of suitable catalysts, such as titanium tetrachloride, zinc chloride, boron trichloride, etc., at temperatures of about 450 to about 500 C or more to form B-stage or partially polymerized polymers which, in final operation, can be molded and completely cured at about 2,000 psi for 4 hours at 450 C, for example, to form thermoset, high temperature- 'resistant polymeric products useful for a wide variety of applications, such as in the preparation of high temperature-resistant materials, etc., as more completely described in Miller application entitled Polymerization of Aromatic Nitriles, Ser. No. 177, l 69, filed Sept. 1, l97l, which is incorporatedherein in its entirety. The completely cured products can be machined to produce a wide variety of parts, such as housings, liners and impellers for pumps useful for handling a number of organic liquids, such as alcohols, ketones, ethers, amines, etc. When compounded with glass fibers, asbestos, etc., the B-stage resins can be employed in preparing solvent resistant pipe suitable for carrying methyl alcohol, ethyl alcohol, acetone and corrosive gases, such as chlorine, etc. The 1,3,5-triazine products of this invention can also be employed in preparing heat resistant semiconductor materials as more fully described in Karguin et a1, U.S. Pat. No. 3,164,555.

Typical of the 1,3,5-triazine products formed by the process of this invention is 2,4,6-tris(3-cyanophenyl)- 1,3,5-triazine (Il) prepared from isophthalonitrile. The formula of (II) is as follows:

ON 7 ON The products of this invention are insoluble'in most organic solvents; however, they exhibit limited solubility in hot xylene, acetonitrile and acetone, etc.

The following example illustrates one embodiment of this invention and is to be considered not limitative.

EXAMPLE I In this example l,3-dicyanobenzene was trimerized using CuCO -Cu(OH) as a catalyst. The reaction was carried out in a'stainless steel tube, 3/8 inch diameter by 5 inches in length with cap fittings'at each end. The materials were weighed into the tube which was then evacuated, back filled with nitrogen and sealed after which the tube was placed in a rocking mechanism arranged to run at approximately 10 rpm. The assembly was placed in a preheated oven and was maintained at 400 C for 4 hours. After the tube had been removed from the oven, cooled and opened, the contents were removed for analysis. Pertinent details relating to this experiment are set forth in Table I which follows:

CuCO: Cu(OH) -Baker Analyzed Reagent Cat. No. 1786, Lot No. 25746. Assay Cu.55.8%

Identified by infrared analysis as 2,4,6-tris(3-cyano-phenyl)l,3,5- triazine.

What is claimed is:

l. A process for preparing an aromatic substituted 1,3,5-triazine which comprises heating an aromatic nitrile at a temperature of from about 180 to about 450 F in the presence of a copper carbonate catalyst.

2. The process of claim 1 wherein the copper carbonate catalyst is selected from the group consisting of:

a. CuCO "Cu(Ol-l) and c. Mixtures of (a) and (b) 3. The process of claim 1 wherein the unconverted nitrile is removed from the formed triazine product by sublimation.

4. The process of claim 1 wherein the unconverted nitrile is removed from the formed triazine product by extraction with a solvent.

5. The process of claim 1 wherein the said nitrile is heated in the presence of a catalyst at a temperature of from about 180 to about 450 C.

6. The process of claim 1 wherein the catalyst is employed is CuCO 'Cu(OH) 7. The process of claim 1 wherein a catalyst employed is 2CuCO 'Cu(OH 8. The process of claim 1 wherein the catalyst is removed from the formed 1,3,5-triazine product by extraction with a solvent.

9. The process of claim 1 wherein the said catalyst is removed from the formed 1,3,5-triazine product by extraction with ammonium hydroxide.

10. The process of claim 1 wherein the said aromatic nitrile has the formula:

wherein R is selected from the group consisting of hydrogen, alkyl of from one to 10 inclusive carbon atoms, amino, nitro, hydroxy, carboxyl, and halogen, and n is an integer of from 1 to 4 inclusive.

11. The method of claim 1 wherein the said aromatic nitrile has the formula:

to about 450 C in the presence of CuCO Cu(OH) and removing the uncovered isophthalonitrile from the triazine product by sublimation. 

2. The process of claim 1 wherein the copper carbonate catalyst is selected from the group consisting of: a. CuCO3.Cu(OH)2, and b. 2CuCO3.Cu(OH)2, and c. Mixtures of (a) and (b)
 3. The process of claim 1 wherein the unconverted nitrile is removed from the formed triazine product by sublimation.
 4. The process of claim 1 wherein the unconverted nitrile is removed from the formed triazine product by extraction with a solvent.
 5. The process of claim 1 wherein the said nitrile is heated in the presence of a catalyst at a temperature of from about 180* to about 450* C.
 6. The process of claim 1 wherein the catalyst is employed is CuCO3.Cu(OH)2.
 7. The process of claim 1 wherein a catalyst employed is 2CuCO3.Cu(OH)2.
 8. The process of claim 1 wherein the catalyst is removed from the formed 1,3,5-triazine product by extraction with a solvent.
 9. The process of claim 1 wherein the said catalyst is removed from the formed 1,3,5-triazine product by extraction with ammonium hydroxide.
 10. The process of claim 1 wherein the said aromatic nitrile has the formula:
 11. The method of claim 1 wherein the said aromatic nitrile has the formula:
 12. The process of claim 1 wherein the said nitrile is isophthalonitrile.
 13. The process of claim 1 wherein from about 0.1 to about 50 weight percent of the said catalyst is employed based on the weight of the nitrile.
 14. The process for the preparation of 2,4,6-tris-(3-cyanophenyl)-1,3,5-triazine which comprises heating isophthalonitrile at a temperature of from about 180* to about 450* C in the presence of CuCO3.Cu(OH)2 and removing the uncovered isophthalonitrile from the triazine product by sublimation. 